1. Field of the Invention
The present invention relates to a method for forming a thin film. More particularly, the present invention relates to a method of forming an amorphous silicon thin film.
2. Description of the Related Art
In manufacturing semiconductor devices, various apparatuses and processes have been developed to provide a high quality thin film on a substrate. Several methods have been used to form thin films, employing surface reaction of a semiconductor substrate. The methods include vacuum evaporation deposition, Physical Vapor Deposition (PVD), Molecular Beam Epitaxy (MBE), different variants of Chemical Vapor Deposition (CVD) (including low-pressure and organometallic CVD and plasma-enhanced CVD), and Atomic Layer Epitaxy (ALE). ALE was studied extensively for semiconductor deposition and electroluminescent display applications, and has been more recently referred to as Atomic Layer Deposition (ALD) for the deposition of a variety of materials.
An exemplary physical vapor deposition method is sputtering. However, sputtering tends to exhibit a poor step-coverage. Thus, sputtering may not be used for forming a film having a uniform thickness on a surface with protrusions and depressions, particularly in high aspect ratio applications like DRAM capacitors.
In a chemical vapor deposition process, two or more reactant gases are reacted with one another over a surface of a substrate. One or more resulting compounds that are produced by the gas phase reaction are deposited on the surface of the substrate. Chemical vapor deposition typically provides a film having a good step-coverage, but has a dependency on temperature and gas supply uniformity. In addition, chemical vapor deposition causes less damage to a substrate than physical vapor deposition. Chemical vapor deposition can also be used in mass production of thin films at a relatively low cost.
Generally, ALD involves sequential introduction of separate pulses of at least two reactants until a layer of a desired thickness is deposited through self-limiting adsorption of monolayers of materials on a substrate surface. For example, in forming a thin film including an AB material, a cycle of four sequential steps of: (1) a first reactant gas A supply; (2) an inert purge gas supply; (3) a second reactant gas B supply; and (4) an inert purge gas supply is repeated. An atomic layer deposition (ALD) method can be performed at a low temperature, for example, a temperature lower than 400° C.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form prior art already known in this country to a person of ordinary skill in the art.